HP Laserjet 4 Manual

PC (Tray 2) and LC (Tray 3) Tray Size Sensing
System
Trays inserted into the printer trigger specific microswitches,
which define the tray size (see Table 5-4). Refer to Figure 7-1 for
location.    
Switch Description PCA
SW601 Door Open Sensing Switches (front and rear) Paper Control PCA
SW602 Test Print Switch Paper Control PCA
SW603 PC tray (Tray 2) Size Sensing Switches Paper Control PCA
SW604 PC tray (Tray 2) Size Sensing Switches Paper Control PCA
SW605 PC tray (Tray 2) Size Sensing Switches Paper...

Motors       
The DC Controller controls the Exhaust Fan, the Main Motor,
and the Laser/Scanner Motor. The remaining motors and
solenoids are controlled by State Machines on the motor’s
assembly. The condition of these motors and solenoids is
monitored by the DC Controller through serial data lines.  
The Main Motor (M1) rotates after any printer door is opened and
closed, during the Warm-up period, the Initial Rotation period,
the Print period, or the Last Rotation Period. The Scanner Motor
(M5) is...

Paper Jam Detection 
The Input/Registration Sensor (PS1) and the Paper Exit Sensor
(PS3) detect paper moving through the printer. If a paper jam is
detected, the DC Controller PCA immediately stops the printing
process and 13 PAPER JAM or REMOVE PAPER JAM message is
displayed. A paper jam can be detected under any of the following
conditions:
•Input Paper Delay Jam:  When paper does not reach the
Input  Paper Sensor (PS1) within the required time.
•Input Paper Stationary Jam:  When paper does not clear...

Formatter System   
The formatter is responsible for the following:
•Receiving and processing ASCII data from printer interfaces.
•Monitoring front panel input and relaying printer status
information (through the front panel and bi-directional I/O).
•Developing/coordinating data placement and timing with the
print engine.
•Storing font information.
•Communicating with the host computer.
The Formatter PCA can be divided into three functional areas:
•I/O Control
•Memory/Memory Management
•Data Processing...

Figure 5-5 Formatter PCA—Functional Areas
Functional Overview  5-13 

Memory Management
The printer uses several different types of memory. This memory
can be divided into two different categories, Read Only Memory
(ROM) and Random Access Memory (RAM). ROM memory
consists of the  memory located on the Formatter PCA and any
font cartridges that may be installed in the printer. RAM memory
consists of RAM memory resident on the Formatter PCA, SIMM
memory installed in the printer, and the Non-Volatile Memory
(NVRAM) located on the Formatter PCA.
In general, the ROM is...

PJL Overview 
Printer Job Language (PJL) is an integral part of configuration,
in addition to the standard Printer Command Language. With
standard I/O cabling, PJL allows the printer to perform functions
such as:
•Allowing the printer to talk to the host computer through a
Bi-directional parallel connection. The printer can tell the host
such things as the control panel settings, and allow the control
panel settings to be set from the host.
•Dynamic I/O switching allows the printer to be configured
with...

Image Formation System
Laser printing requires the interaction of several different
technologies (such as electronics, optics, and
electro-photographics) to provide a printed page. Each process
functions independently and must be coordinated with all other
printer processes. The image formation process centers around
the photosensitive drum and consists of six stages:
1. Cleaning 4. Developing
2. Conditioning 5. Transferring
3. Writing 6. Fusing
The toner cartridge houses the cleaning, conditioning, and...

Photosensitive Drum 
The photosensitive drum is the “heart” of the Image Formation
System. The special properties of this drum allow an image to be
formed on the drum’s surface and then transferred to paper. The
drum is an extruded aluminum cylinder. The outside of the
cylinder is coated with a layer of organic-photoconductive
material (OPC) which is non-toxic. The aluminum base of the
photosensitive drum is electrically connected to ground potential
(see Figure 5-7).
Drum Sensitivity  
The OPC material...

Cleaning Stage  
During the cleaning stage of the image formation process, the
drum’s surface is physically cleaned, preparing it to hold an
image. During printing, the drum is rotating constantly making
several complete rotations per printed page. Before forming the
image for a given section of print, a cleaning blade removes toner
from the previous rotation of the drum. The excess toner is stored
in the toner cartridge where it is prevented from being used in
later print jobs. 
Figure 5-8 Drum Cleaning...